Image-forming machine



April 14, 1964 F. P. ALLES IMAGE-FORMING MACHINE CS Sheets-Sheet 1 Filed April 24, 1962 FIG.!

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FIG. 7

FRANCIS PETER ALLES ATTORNEY April 14, 1964 F. P. ALLES 3,128,498

IMAGE-FORMING MACHINE Filed April 24, 1962 3 Sheets-Sheet 2 as g 64 g Q as ,as 1o INVENTOR FRANCIS PETER ALLES y 2 1 EM ATTORNEY A ril 14, 1964 F. P. ALLES IMAGE-FORMING MACHINE 3 Sheets-Sheet 3 Filed April 24, 1962 FIG.4

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INVENTOR FRANCIS PETER ALLES BY 73M ATTORNEY United States Patent )1 3,128,498 IMAGE-FORMING MACHINE Francis Peter Alles, Basking Ridge, N.J., assignor to E. I. du Pont de N emours and Company, Wilmington, Del., a corporation of Delaware Filed Apr. 24, 1962, Ser. No. 189,891 13 Claims. (Cl. 18-1) This invention relates to a machine for obtaining a clear or light-transmitting image in an opaque pressure-clearable film.

In Bechtold US. Patent 2,957,791 methods are described for selectively clarifying the opaque, pressureclearable films covered by said patent that include pressing the films against a copper engraving, and placing the film in a typewriter, Without an inking ribbon, and typing directly on it. The pressure-clearable films can be placed against type in a proofing press, and the roller passed over the type to produce a clear image of the type in the film. The resultant clear image-bearing elements can then be used as negatives for photoprinting.

An object of this invention is to provide a simple and effective machine for subjecting an opaque, pressureclearable film to image transfer contact with a relief image. A related object is to provide an improved machine for obtaining clear images in such a film by contacting them with relief printing forms, e.g., type matter, and/or halftones. Yet another object is to provide such a machine which results in clear, sharp images which faithfully reproduce the surface of the relief printing form. A further object is to provide such a machine which is simple in construction, easy to operate and gives uniform, dependable results. A still further object is to provide such an apparatus which can be manufactured economically.

The machine of this invention in its broader aspects comprises a plate adapted to support a relief printing form and an opaque, pressure-clearable film in contact with the relief surface, a frame member mounted above and suspended across the printing form adapted to hold a multiplicity of spring fingers of small coactive area in contact with the upper surface of the film and press the lower pressure-clearable surface against the relief surface, and means for allowing relative motion of the plate support and the frame member bearing the spring fingers to subject the'film to a stroking pressure from said fingers. Additionally, the machine is provided with means for changing the position of the spring fingers laterally by a predetermined amount to insure complete and uniform coverage of the whole surface of the film and underlying type form. Preferably, the machine is provided with a vacuum frame about the form and adapted to hold the pressuresensitive film in contact with the surface of the relief.

The invention will now be described with reference to the accompanying drawings which constitute a part of this application. In the drawings:

FIG. 1 is an isometric View of one form of machine with a printing form in place and parts in broken-away construction,

FIG. 2 is a plan View of an alternative form of a machine,

FIG. 3 is a front elevation of the alternative form,

FIG. 4 is a side elevation of the alternative form,

FIG. 5 is a plan view of a segment of the spring fingers,

FIG. 6 is an elevation of the spring fingers,

3,128,498 Patented Apr. 14, 1964 FIG. 7 is an end elevation of the transverse block support with assembled spring fingers and adjusting plate, and

FIG. 8 is an end elevation of the transverse block support with an alternative adjustment plate.

Reference is now made to FIG. 1 of the drawing which illustrates one practical embodiment of the invention. In this figure, and in the other figures of the drawing, similar reference numerals refer to similar parts throughout the several figures. In FIG. 1 the image forming machine comprises a bedplate 10 which carries a relief printing form 11 on which is laid a pressure-clearable film 12. Fastened to the bedplate in any suitable manner are vertical supports 13 which carry guide rails 14 which extend along the sides of the bedplate. T'hese guide rails are pro vided with suitable stop collars 15 which are fastened to guide rails by means of set screws 16. Slideably mounted on the guide rails is a transverse frame 17 having end plates 18 which are provided with suitable holes 19 which interfit with the guide rails. Extending between and fastened to the end plates are transverse rails 20 on which there are slideably mounted bearing supports 21. The inner surface of these bearing supports are provided with vertical grooves 22 which are adapted to receive transverse support block 23. The bottom surface of this support block is provided with a row of spring fingers 24 which are attached to the support block by means of a fastening plate 25 which is held in position by suitable screws 26.

On the sides of the transverse support block are transverse spring adjusting plates 27. These plates have a plurality of elongated holes 28 through which extend bolts 29 that are threadably engaged in the sides of the support block. This arrangement of parts is shown more fully in FIG. 7 of the drawing although the form illustrated in FIG. 1 is that shown in FIG. 8. The bottom inner end of the plates are provided with a groove 30 that is adapted to receive the extended upper end of the spring fingers.

The transverse rails are provided with springs 31 which surround the rails and press against the inner face of the bearing supports and suitable collars 32 that are fastened to the transverse rails by set screws 33.

Ratchet wheel 34 is disposed near one end of the transverse frame between endplate 18 and the bearing support 21. This ratchet wheel has affixed thereto a suitable shaft (not shown in FIG. 1) the inner end of which is threaded for threadable engagement with the bearing support. The opposite end of this shaft is smooth and extends through the endplate. A crank wheel 35 is suitably fastened to the outer end of the shaft. The crank wheel in turn is provided with a suitable crank handle 36. Between the ratchet wheel and the inner surface of the endplate and pivotally mounted on the shaft is a cam arm 37. Pivotally mounted on this cam arm is a pawl 38, the end of which engages the ratchet Wheel. The other end of this pawl has mounted thereon a spring pintle 39. A similar pintle is fastened to the cam arm and mounted on these pintles is spring 41. As shown in FIG. 1, the outer end of the cam arm has a lateral extension 42 on which is fastened a pintle 43 on which there is journalled a roller 44. This roller is adapted to engage with the surfaces of cams 45 which are adjustably mounted on the bedplate in any suitable'manner. As shown in FIG. 1, these cams are disposed in a longitudinal channel 46 in the bedplate. The cams can be fastened in this channel in any suitable manner, for example, by means of threaded bolts (not shown) which extend through the adjusting slots 47.

an impervious support.

In operating the machine shown in FIG. 1 of the drawing, the printing form .11 is placed on the bedplate and, if necessary, fastened to it by any suitable means. The pressure-clearable film is then laid over the relief surface of the printing film. The pressure-clearable film can be taped to the printing form or to the bedplate by means of any suitable pressure-sensitive sealing tape. Alternatively, the film to be used can be held in place by vacuum; for example, a vacuum frame 43 having a suitable sealing gasket 4% can be placed around the printing block. A protective sheet 5% can then be placed over the vacuum frame but is not essential with films having Air can then be withdrawn in the space between the vacuum frame, the printing block and the film or the protective cover sheet in any suitable manner, e.g., by providing suitable connecting passages and hoses or conduits connected to a vacuum pump.

The spring fingers are then adjusted to the desired height so that the bottom actuating surface presses against the pressure-clearable film or protective sheet with the desired amount of pressure. This may vary somewhat depending on the nature of the surface of the relief. It may differ with halftones and line or type matter.

The transverse frame is then grasped and actuated to and fro on the guide rail-s. As the transverse frame and associated mechanism is reciprocated, the bottom surfaces of the spring fingers will have a stroking action on the pressure-clearablc film. The frame can be actuated by hand or can be actuated automatically by means of hydraulic cylinders or reversible motors suitably connected to the frame so that it can be reciprocated back and forth along the guide rails.

At the end of each stroke, the cam roller will engage the respective cam to actuate the ratchet wheel and thereby move the transverse support block laterally a short distance.

Alternatively, one of the cams can be removed so that the transverse support block can be moved a small increment of distance only after a complete double movement of the transverse frame.

The initial position of the transverse support block can be adjusted by turning the crank by means of the crank handle as.

As shown in FIG. 5 of the drawing, the spring fingers are narrow, elongated portions of a single sheet and the bottom surface of each finger segment has a depressed surface area of even lesser coactive area than that defined by the width of the individual finger segments. These depressed areas are designated 24.

In FIGS. 2, 3 and 4 of the drawing there is disclosed on alternative machine. This machine differs from that shown in FIG. 1 in that the bedpl ate, printing form, pressure-clearable film, and associated parts are adapted to be moved longitudinally with respect to the transverse support block and spring fingers. Thus, the transverse frame is fixed and the bedplate capable of movement back and forth in a horizontal plane.

In the machine as shown in FIGS. 2, 3 and 4 of the drawing, a horizontal rectangular frame 6% carries on its upper surface along one side a V-shaped ridge 6 1 that is adapted to receive a slideable bedplate 62.. The bottom surface of the bedplate is provided with a suitable coacting groove member 63 which interfits with and rides on the V-shaped ridge. The edge of the bedplate opposite the V-shaped groove members has mounted thereon suitable pintles 64 on which there are journalled rollers 65. These rollers are adapted to roll along the upper surface of the horizontal frame. A rectangular frame member 66 is fastened to the slide-able bedplate in any suitable manner. A suitable printing form, not shown in FIGS. 2 4, is adapted to be placed on the surface of the slideable bedplate and within the confines of the rectangular frame.

Vertical support members are mounted on the horizontal frame near its outer side edges and preferably near the central part of the sides. These supports 60 can be integral with the frame and can be welded, bonded, or otherwise affixed to the frame member. Extending between these vertical supports are transverse guide rails 68 on which there are slideably mounted end plates 69. The ends of these rails can be threaded and held in place by means of nuts 70. Extending between these end plates and fastened thereto is a transverse cross-brace 7 1 on which there is adjustably mounted a transverse support block 72. The ends of this support block fit into a vertical groove 73 in the inner surface of each of the endplates. The transverse support block is fastened to the cross-brace by means of adjusting screws 74 that have threadable engagement with threaded holes in the support block. These adjusting screws extend through the cross-brace and through suitable threaded collars 75 between the bottom surface of said cross-brace and the top surface of the support block. The collars are adjusted by means of radial holes 76, disposed about the peripheries into which a rod or spanner may be inserted to turn them. The row of spring fingers 77 is fastened to the bottom surface of the support block in the same manner as described above with reference to the machine shown in FIG. 1. On the sides of the support block there are similarly mounted transverse spring adjusting plates 78.

These plates have elongated holes 79 extending therethrough, through which there are inserted bolts 80 that threadably engage the support block.

Mounted on the transverse rail 68 are collars 81 that are fastened in position by means of suitable set screws 82. Springs 83 extend around these rails and press against the respective collars and inner surface of the endplates.

The transverse cross-brace can be fastened to the endplates in any suitable manner, e.g., by means of countersunk screws 34 which threadably engage holes in the endplates.

A ratchet Wheel 85 disposed between one of the endplates and one of the vertical supports, is provided with a suitable shaft the inner end of which has a screw thread for engagement with coactive screw threads (not shown) in the endplate. The outer end of the shaft 85' has a. smooth surface and extends through a suitable hole 86 in the endplate] Between the ratchet wheel and the endplate, and journalled on the shaft, is a cam arm 87. Pawl 88 is pivotally mounted on this cam arm and has a detent 89 that engages with the ratchet wheel. If desired, this pawl can be provided with a suitable pintle on which there is mounted one end of a spring, the other end of which can be mounted on a similar pintle on the cam arm in a manner similar to that shown in FIG. 1. For the sake of clarity, the details of this are not given in FIGS. 24.

The cam arm has a lateral section which carries a pintle 99 on which there is journalled a cam roller 91. This cam roller is adapted to coact with suitable cams 92 mounted on the longitudinal side rails 93 that are fastened to the slideable bedplate in any suitable manner.

As shown in FIG. 4, an outer end of these side rails is provided with an upwardly extending arm portion 94. Extending between and fastened to this arm portion is a transverse handle 95.

If desired, the outer end of the shaft of the ratchet wheel can be provided with a crank so that the ratchet wheel can be turned by the operator at any desired moment. A crank and crank handle like that shown in FIG. 1 can be used.

The machine of FIGS. 2, 3 and 4, in general, operates in essentially the same way as that of FIG. 1. To be more specific, a printing form is placed on the slideable bedplate and a sheet of opaque pressure-clearable film is stretched across the top of the printing form. The bedplate is then reciprocated to and fro instead of the transverse frame of FIG. 1. The spring fingers, ratchet wheel, etc. operate essentially in the same Way as in the area s98 machine of FIG. 1 and to avoid repetition, the details are not given again.

The distance the transverse support block is maintained above the surface of the printing form can be adjusted by turning screws 74 and collars 75.

With particular reference to FIG. 1, the rails 14 can, if desired, be mounted in blocks that can be adjusted upwardly and downwardly, thus permitting further adjustment of the distance of the spring fingers from the surface of the printing form. These blocks can be spring loaded. The rails 68 can be mounted similarly for adjustment in vertical supports 60'.

In FIG. 8 of the drawing, there is shown an alternative form of support block. In this form the adjusting plate 25 is wider than the block and contacts with the slanting bottom surfaces of the spring fingers. Its distance from the bottom of the block 23 is adjusted by a suitable shim 96 and locked by means of screws 26.

By substituting shims of different thicknesses, one can attain further adjustment in the action of the spring fingers.

The various structural parts of the machines described can be made of conventional materials of construction. For most of the members and parts, steel, steel alloys, brass, aluminum, aluminum alloys, and high strength plastics, e.g., polyacetal resins, glass fibre laminates, nylon, etc. may be employed. For the spring fingers, it is preferred to use hardened beryllium copper, but Phosphor bronze, spring steel, etc. may be employed. The wearing surface of the fingers may be plated or coated with hard, abrasion-resistant material, e.g., chromium, rhodium, tungsten carbide, stellite, etc. The base plate, bearing blocks, corner supporting members and transverse blocks, etc., can be made of cast iron or die cast aluminum.

Various types of opaque pressure-clearable films can be used in the apparatus of this invention. As previously stated, suitable pressure-clearable films are described in Bechtold U.S. Patent 2,957,791. Other useful supported and unsupported pressure-clearable films are described in U.S. Patents 2,846,727, 2,848,752, and in assignees U.S. Application Ser. No. 63,953, Oct. 21, 1960.

The opaque pressure-clearable films described in Bechtold U.S. Patent 2,957,791 and in the Bechtold patents referred to therein, have also been called opaque pressureclarifiable or pressure-coalescible films, but are more aptly termed opaque pressure-clearable films since the opaque areas which are highly opaque are converted by means of pressure into clear areas readily transparent to visible light. The films are also clearable by heat and by heat and pressure.

The pressure-clearable films or coatings of the Bechtold patents which constitute preferred materials for use in this invention are porous, opaque, non-fibrous, of low bulk density and are composed of partially coalesced discrete particles of a hydrophobic organic addition polymer having a wholly carbon chain, a molecular weight of at least 10,000 and being taken from the group consisting of vinyl and vinylidene addition polymers, said film having I an open-cell structure characterized by microscopic voids communicating with the surface and containing 20% to 80% by volume of open-cell pores, said film having a permeability to water vapor of at least 10 times greater than that of corresponding non-porous films of the same polymer and thickness, the opacity per unit of thickness being such that a film thickness of 3 mils and greater has a light-transmission of less than 10% at 4000 A., and increased light transmission at longer wavelengths of light, said film being capable of sustaining a permanent reduction in thickness of at least 20% together with substantial clarification of opaqueness under a pressure of 10,000 pounds per square inch at room temperature. These films are more fully described and defined in Bechtold U.S. Patent 2,957,791 which constitutes part of this disclosure.

After the clarified, or clear, images are formed in the opaque pressure clearable films by using the machines of this invention, the opaque background areas can be increased in optical density by deposition of opaque ma terial in such areas to provide a high-contrast imagebearing layer. These areas being porous are readily coated or impregnated with colorants which fill the open cell voids. Any of the postdensification procedures described in assignees Bechtold U.S. application Ser. No. 63,953 can be used. Thus, the selectively clarified coating can be post-densified in unchanged opaque background areas by in situ deposition of lead sulfide at 50 C. by immersing the coating in aqueous lead nitrate and sodium sulfide solutions with intermediate blotting with porous cardboard, washing in water and drying which gives a dense, black background. Alternatively, the background areas can be post-densified by dyeing for several minutes with 2.5% aqueous solution of an after-chromed dye, Colour Index No. 15,710, at 50 C. for several minutes.

While, for simplicity, the machine described are shown with a double row of off-set spring fingers, it is obvious that a single row or multiple rows of larger number might be employed. In addition, while the machines have been shown as operating in essentially a straight line fashion, the machine can be modified so that the finger assembly can be rotated over the relief plate surface in a horizontal plane or fixed above the relief plate surface and the bedplate rotated beneath the fingers. In a machine with straight line motion of the type shown, it is preferable to have the horizontal relief surface at a slight angle, for instance, up to about 10 to a main axis of the plate or line of travel of the machine. This prevents all of the fingers from dropping below the type surface at the same time and makes for smoother operation.

While the contacting area 24 of the spring fingers, i.e., the spherical surface on the spring fingers, may vary in size, surfaces having radii of about .008 to .016 inch are desirable sizes, because these sizes will clarify a .002 to .003 inch width of line and the smaller characters on most relief printing forms are approximately .003 inch in their smallest dimension. The loading on the spring fingers depends upon the characteristics of the opaque, pressure-clearable film. The load required to clarify a typical such film having a pressure clarifiablc layer of about .0005 inch on a .002 inch polyethylene terephthalate base using a .019 inch radius spherical clarification element, is approximately grams Weight, which will produce substantially minimum optical density. The spring fingers are prestressed to obtain pressure suflicient for clarification; and as shown in the drawings, the depth of penetration below average type height is controlled. on a typical relief printing form, average type height is 0.918 inch $003 inch; and, conveniently, the penetration of the fingers should be from .010 inch to .005 inch below average type height for satisfactory operation.

A convenient spacing of lines obtained with the double row of fingers shown is about .033 inch. Obviously the closer the lines, the fewer the number of passes required to obtain adequate coverage of the entire surface. However, there are limitations on the dimensions of the fingers and slots. The length, width and thickness of the fingers are dictated by the materials used in constructing them, the pressure required for clarification, and the need to prevent excessive lateral movement when the finger passes over a line oriented at an angle to the path or when the type face is curved. The fingers can be separate and inserted in a block. They can be made of resins or superpolymers and have inserts of metal at the area of contact.

To obtain maximum clarification with the machines and fingers described, the fingers should be moved about .001 inch laterally for each successive pass.

The machine of this invention has the advantage that it is simple in construction but dependable in operation. When used as described above, it will faithfully reproduce a printing relief forming a clear and transparent image of the relief in the opaque pressure-clearable film element. The machine has the advantage that it is readily adaptable for obtaining photographic negatives or transparencies from a wide variety of printing reliefs including type forms, engraved plates, photopolymerized printing reliefs, halftones, combined halftones and line printing forms, etc.

Another advantage is that the various parts of the machine are simple in construction, easy to assemble, require little attention to keep them in operative condition, and have good wearing properties. A further advantage is that the machine does not require much space and is relatively inexpensive.

A still further advantage of the ordered method of clarification employed by these machines is that the pressure applied to any one character can be reduced to a minimum and the depth of penetration in shallow relief areas can be controlled. In addition, uniform coverage of the surface to be reproduced is insured.

A particular advantage of the invention is that it permits one to rapidly convert a printing relief into a photographic transparency, accurately reproducing as a clear image all of the fine detail of the relief. The machine has an additional advantage that it does not damage the surface of the relief or type form and gives an adequate, clear image in an opaque pressure-clearable film in a short time. It avoids the use of heavy pressure rollers such as those used in pulling a proof from a bed of type which often damages the type surface and cannot be successfully used where fine rulings are in the printing surface. Still further advantages will be apparent from the foregoing description and accompanying drawings.

I claim:

1. An image-forming machine comprising:

(A) a bedplate adapted to support a relief printing form and an opaque, pressure-clearable film in contact with its relief surface,

(B) a frame member mounted above and suspended across said bedplate,

(C) at least 1 row of yieldable fingers of small coactive area and another row of such fingers with small coactive areas offset from those of the first row held by said frame member and adapted to contact with the upper surface of such a film and press the film against the relief surface of said form, and

(D) means providing reciprocating motion between the bedplate and frame member to subject the film to a stroking pressure from said fingers during the motion.

2. An image-forming machine comprising:

(A) a bedplate adapted to support a relief printing form and an opaque, pressure-clearable film in contact with its relief surface,

(B) a frame member mounted above and suspended across said bedplate,

(C) at least one row of yieldable fingers of small coactive area held by said frame member and adapted to contact with the upper surface of such a film and press the film against the relief surface of said form,

(D) means providing relative motion between the bedplate and frame member to subject the film to a stroking pressure from said fingers during the motion, and

(E) means for laterally adjusting the position of the yieldable fingers with respect to the relief form.

3. An image-forming machine comprising:

(A) a horizontal bedplate adapted to support a relief printing form and an opaque pressure-clearable film in contact With the relief surface,

(B) a frame member having a transverse support block extended across said bedplate,

(C) a row of spring fingers of small coactive area and another row of such fingers with small coactive areas offset from those of the first row adjustably mounted on the bottom surface of said block, the coactive area of the fingers being adapted to contact with the upper surface of such a film and press the lower surface of the film against the relief surface of said form, and

(D) means providing reciprocating motion in a horizontal plane between said bedplate and support block to subject the film to a stroking pressure from said fingers during said motion.

4. A machine according to claim 3 wherein the position of said support block can be adjusted laterally in small increments.

5. A machine according to claim 3 wherein the frame member is provided with a ratchet Wheel, a pawl, and a cam follower and there is a screw connection between the ratchet wheel and support block so that said block can be adjusted laterally in small increments by coaction of the cam follower with a cam surface on the bedplate.

6. An image-forming machine comprising:

(a) a fixed horizontal bedplate adapted to receive a relief printing form and an opaque pressure-clearable film in contact with the relief surface thereof,

(12) vertical supports fixedly mounted on said bedplate having guide rails extending between the supports along each side of the bedplate,

(c) a transverse frame member slidably mounted on said guide rails having a laterally and vertically adjustable support block mounted thereon,

(d) a row of spring fingers of small coactive area mounted on the bottom surface of said support block, the coactive area of the fingers being adapted to contact with the upper surface of such a film and press the lower surface of the film against the relief surface of said form,

(e) a ratchet wheel, spring-biased pawl and a cam arm carried by said frame member,

(f) means carried by said frame member for turning said ratchet wheel and laterally adjusting said block, and

(g) cams mounted on said bedplate to cooperate with said cam arm and separately turn said ratchet wheel and adjust the lateral position of said block.

7. A machine according to claim 6 wherein said support block has means for adjusting the horizontal position and limiting the downward movement of the spring fingers.

8. A machine according to claim 6 wherein said support block has means for adjusting the horizontal position and tension of the spring fingers.

9. A machine according to claim 6 wherein the bedplate carries a vacuum frame which extends around said printing form.

10. An image-forming machine comprising:

(1) a fixed horizontal frame,

(2) a bedplate slidably mounted on said frame and adapted to receive a relief printing form and an opaque pressure-clearable film in contact with the relief surface,

(3) vertical supports fixedly mounted on said frame,

(4) transverse guide rails extending between said supports and across said printing form,

(5) a laterally and vertically adjustable block slidably mounted on said transverse rails,

(6) a row of spring fingers of small coactive area mounted on the bottom surface of said support block, the coactive area of the fingers being adapted to contact with the upper surface of such a film and press the lower surface of the film against the relief surface of said film,

(7) a ratchet wheel carried by said vertical supports and having a screw thread engagement with said block,

(8) a spring-biased pawl and a pawl arm carried by said vertical supports,

(9) a cam roller carried by said arm and a cam carried by said slidable bedplate for actuating cam roller and pawl arm, to turn said ratchet wheel, and

support block has means for adjusting the horizontal po- 10 sition and tension of the spring fingers.

13. A machine according to claim 11 wherein said bedplate carries a vacuum frame which extends around said printing form.

References Cited in the file of this patent UNITED STATES PATENTS La Baiteaux Nov. 25, 1924 Ayres Jan. 9, 1945 Terry May 1, 1945 Schultz Mar. 25, 1958 Ellison et al Mar. 15, 1960 

1. AN IMAGE-FORMING MACHINE COMPRISING: (A) A BEDPLATE ADAPTED TO SUPPORT A RELIEF PRINTING FORM AND AN OPAQUE, PRESSURE-CLEARABLE FILM IN CONTACT WITH ITS RELIEF SURFACE, (B) A FRAME MEMBER MOUNTED ABOVE AND SUSPENDED ACROSS SAID BEDPLATE, (C) AT LEAST 1 ROW OF YIELDABLE FINGERS OF SMALL COACTIVE AREA AND ANOTHER ROW OF SUCH FINGERS WITH SMALL COACTIVE AREAS OFFSET FROM THOSE OF THE FIRST ROW HELD BY SAID FRAME MEMBER AND ADAPTED TO CONTACT WITH THE UPPER SURFACE OF SUCH A FILM AND PRESS THE FILM AGAINST THE RELIEF SURFACE OF SAID FORM, AND (D) MEANS PROVIDING RECIPROCATING MOTION BETWEEN THE BEDPLATE AND FRAME MEMBER TO SUBJECT THE FILM TO A STROKING PRESSURE FROM SAID FINGERS DURING THE MOTION. 